1. Field of the Invention
This invention relates to lined pipe and more particularly to lined pipe wherein the lining is coupled to the outer pipe.
2. Prior Art
In the prior art there exists many methods for making lined pipe wherein the lining is coupled to the outer pipe and each of such methods has its own disadvantages and drawbacks. The most simplist method is to make the outer diameter of the lining approximately the same as the inside diameter of the outer pipe and then press the lining into the outer pipe. This method has certain disadvantages in that the lining may crack during the pressing process if the lining is made from a rigid material, the lining may eventually work free of the outer pipe since there is no real coupling between the lining and the outer pipe except friction and expensive machinery is required to press the lining into the outer pipe.
Another method for coupling the lining to the outer pipe is to score the inner surface of the outer pipe, press the lining which has an outer diameter which is substantially equal to the inner diameter of the outer pipe into the outer pipe and then heat the outer pipe to cause the lining to flow into the scoring and form a coupling thereinbetween. This method has most of the disadvantages of the above described method except that it overcomes the disadvantage of the eventual working free of the lining from the outer pipe; but this method provides additional disadvantages in that it requires more equipment than the previously described method and can only be used with metallic outer pipes and linings which can be melted.
A third method for coupling the lining to the outer pipe is to inject a thermal-setting adhesive which can bond to both the lining and the outer pipe between the lining and the outer pipe to form an adhesive bond between the lining and the outer pipe. This method may overcome some of the disadvantages described above but it has a particular disadvantage in that it can be only used with adhesives which can bond to the materials of both the lining and the outer pipe.
A fourth method for coupling the lining to the outer pipe includes the steps of forming two sections of lining wherein each of the sections has one flanged end and the unflanged ends of the lining are formed so that one can fit into the other. These two sections of lining are then inserted into opposite ends of the outer pipe and bonded together. This method again overcomes some of the above described disadvantages but it too creates its own disadvantages. The major disadvantage of this method is that it requires specially formed sections of lining which may be expensive and time consuming to manufacture. Another problem is that if the pipe must be shortened at the point of installation, the coupling is destroyed by cutting off one of the flanged ends.